Thomas and Ann lived at the Second River settlement in Essex County, which was named Belleville in 1797.
James Ennis Sr. of New Barbadoes Neck, Bergen County, New Jersey nominated his son James and "nephew William Duval" as executors of his will in 1797. James was a son of William Ennis, also of New Barbadoes Neck, who named wife Hanah, and children James and Ann, as well as William Jr. and Mary, in his will in 1771. Hassel Brouwer gave bond for James Ennis to administer the estate with the will annexed in 1776. 
Unfortunately, the William Du Vall family bible from which this information comes specialized in the death dates of his siblings, not so much their other vitals.
Ann (Ennis) Du Vall died on 16 May 1809, age 65.
↑ 1.01.11.2 Raymond, James Loder, extracts from the family bible of William Du Vall of 49 Maiden Lane. The New York Genealogical And Biographical Record. New York: New York Genealogical and Biographical Society, 1891, 22:105-6.
↑ Abstract of the will of James Ennis Sr., 1797. Documents Relating to the Colonial, Revolutionary and Post-Revolutionary History of the State of New Jersey: First Series-Vol. XXXVIII : Calendar of New Jersey Wills, Administrations, Etc. Volume IX, 1796-1800. Newark, New Jersey : The Daily Journal Establishment, 1880-1949, p. 123; FamilySearch, FHL Film # 7,809,466, image 435.
↑ Abstract of the will of William Ennis, 1771/1776. Ibid., Vol. XXXIV, Calendar of New Jersey Wills, Administrations, Etc. Volume V, 1771-1780, p. 166; FamilySearch, FHL Film # 7,809,468, image 478.
"New Jersey Births and Christenings, 1660-1980," database, FamilySearch (https://familysearch.org/ark:/61903/1:1:FZ6W-C8P : 11 February 2018), Thomas De Vael in entry for Thomas De Vael, 08 Mar 1784; citing , reference ; FHL microfilm 1016878, 974.9 B2G, 0982039.
It may be possible to confirm family relationships with Ann by comparing test results with other carriers of her mitochondrial DNA.
However, there are no known mtDNA test-takers in her direct maternal line.
It is likely that these autosomal DNA test-takers will share DNA with Ann: